Protonic conduction of CsH2PO4 and its composite with silica in dry and humid atmospheres

Otomo, Junichiro; Minagawa, Naohisa; Wen, Ching–ju; Eguchi, Koichi; Takahashi, Hiroshi

doi:10.1016/s0167-2738(02)00746-4

Cited by 209 publications

(167 citation statements)

References 23 publications

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“…We attribute this to the polymorphic behavior of CsPO 3 , which is known to crystallize in long-chain, cyclic and other forms depending on the details of the thermal history and preparation methods. 15 On the basis of the work of Osterheld and Markowitz, 10 who used the Jones method 16 to analyze the dehydration products of CsH 2 PO 4 obtained under similar dry conditions, we conclude that the product phase generated in this study is long-chain CsPO 3 .…”

Section: X-ray Powder Diffraction Analysis Of Reaction Productsmentioning

confidence: 59%

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Dehydration behavior of the superprotonic conductor CsH2PO4 at moderate temperatures: 230 to 260 °C

et al. 2007

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The dehydration behavior of caesium dihydrogen phosphate CsH 2 PO 4 was investigated in the temperature range of 230 uC to 260 uC under high humidity, conditions of particular relevance to the operation of fuel cells based on this electrolyte. The onset temperature of dehydration was determined from changes in ionic conductivity on heating and confirmed by weight change measurements under isothermal conditions. The relationship between the onset temperature of dehydration (T dehy ) and water partial pressure (p H 2 O ) was determined to be log(p H 2 O /atm = 6.11(¡0.82) 2 3.63(¡0.42) 6 1000/(T dehy /K), from which the thermodynamic parameters of the dehydration reaction from CsH 2 PO 4 to CsPO 3 were evaluated. The dehydration pathway was then probed by X-ray powder diffraction analysis of the product phases and by thermogravimetric analysis under slow heating. It was found that, although the equilibrium dehydration product is solid caesium metaphosphate CsPO 3 , the reaction occurs via two overlapping steps: CsH 2 PO 4 A Cs 2 H 2 P 2 O 7 A CsPO 3 , with solid caesium hydrogen pyrophosphate, Cs 2 H 2 P 2 O 7 , appearing as a kinetically favored, transient phase.

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Section: X-ray Powder Diffraction Analysis Of Reaction Productsmentioning

confidence: 59%

“…228 uC. [1][2][3][4] The superprotonic phase of CsH 2 PO 4 exhibits proton conductivity greater than 10 22 S cm…”

Section: Introductionmentioning

confidence: 99%

Dehydration behavior of the superprotonic conductor CsH2PO4 at moderate temperatures: 230 to 260 °C

et al. 2007

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“…25 The raw impedance data collected both by Boysen et al 26 and Otomo et al 25 exhibit the features described in Fig. 1, supporting the hypothesis that the analysis procedure employed by Park 29 was not applicable to the high temperature phase.…”

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confidence: 57%

Solid acid proton conductors: from laboratory curiosities to fuel cell electrolytes

et al. 2007

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The compound CsH 2 PO 4 has emerged as a viable electrolyte for intermediate temperature (200-300 1C) fuel cells. In order to settle the question of the high temperature behavior of this material, conductivity measurements were performed by two-point AC impedance spectroscopy under humidified conditions (p[H 2 O] = 0.4 atm). A transition to a stable, high conductivity phase was observed at 230 1C, with the conductivity rising to a value of 2.2 Â 10 À2 S cm À1 at 240 1C and the activation energy of proton transport dropping to 0.42 eV. In the absence of active humidification, dehydration of CsH 2 PO 4 does indeed occur, but, in contradiction to some suggestions in the literature, the dehydration process is not responsible for the high conductivity at this temperature. Electrochemical characterization by galvanostatic current interrupt (GCI) methods and three-point AC impedance spectroscopy (under uniform, humidified gases) of CsH 2 PO 4 based fuel cells, in which a composite mixture of the electrolyte, Pt supported on carbon, Pt black and carbon black served as the electrodes, showed that the overpotential for hydrogen electrooxidation was virtually immeasurable. The overpotential for oxygen electroreduction, however, was found to be on the order of 100 mV at 100 mA cm À2. Thus, for fuel cells in which the supported electrolyte membrane was only 25 mm in thickness and in which a peak power density of 415 mW cm À2 was achieved, the majority of the overpotential was found to be due to the slow rate of oxygen electrocatalysis. While the much faster kinetics at the anode over those at the cathode are not surprising, the result indicates that enhancing power output beyond the present levels will require improving cathode properties rather than further lowering the electrolyte thickness. In addition to the characterization of the transport and electrochemical properties of CsH 2 PO 4 , a discussion of the entropy of the superprotonic transition and the implications for proton transport is presented.

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“…(1) Hydrolysis of DPDES Compared with silicon alkoxides such as Si(OR) 4 or CH 3 Si(OR) 3 (R 5 CH 3 , C 2 H 5 ), the hydrolysis and condensation reactions of PhSi(OR) 3 From Eq. (2), the integrated first-order rate law is represented as follow: (2) Preparation of Ph 2 SiO-Based Core Particle DPDES was hydrolyzed by using 0.1 wt.% HCl solution at 701C for 3 h, and then TEOS was added to the partially hydrolyzed DPDES sol solution and further stirred at 701C for 2 h. 60Ph 2 SiO Á 40SiO 2 particles were prepared following the procedure shown in Fig.…”

Section: Resultsmentioning

confidence: 99%

Formation of a High Conductivity Fuel Cell Electrolyte by Pressing Diphenylsiloxane‐Based Inorganic–Organic Hybrid Particles

Daiko

Sakakibara

Sakamoto

et al. 2009

Journal of the American Ceramic Society

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An inorganic-organic nanohybrid particle with a two-dimensional chain structure, diphenylsiloxane-silica (Ph 2 SiO-SiO 2 ), was prepared by sol-gel process using diphenyldiethoxysilane (DPDES) and tetraethoxysilane (TEOS), and a high proton conducting polymer of poly(2-acrylamido-2-methyl-1-propane sulfonic acid) (PAMPS) was deposited on the Ph 2 SiO-SiO 2 particles via layer-by-layer assembly. A flexible sheet-like electrolyte was successfully obtained from the resulting PAMPSdeposited particles by pressing. The proton conductivity of the sheet prepared using unmodified Ph 2 SiO-SiO 2 particles was lower than 10 À9 S/cm at 801C. On the other hand, the PAMPSdeposited samples showed proton conductivities B7 orders of magnitude higher than those of the sample prepared using unmodified particles, and their conductivity reached about 1 Â 10 À2 S/cm at 801C and 80% relative humidity. This is ascribed to the PAMPS layer being concentrated at the particle interfaces, which percolated throughout the monolithic sample.

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Protonic conduction of CsH2PO4 and its composite with silica in dry and humid atmospheres

Cited by 209 publications

References 23 publications

Dehydration behavior of the superprotonic conductor CsH2PO4 at moderate temperatures: 230 to 260 °C

Dehydration behavior of the superprotonic conductor CsH2PO4 at moderate temperatures: 230 to 260 °C

Solid acid proton conductors: from laboratory curiosities to fuel cell electrolytes

Formation of a High Conductivity Fuel Cell Electrolyte by Pressing Diphenylsiloxane‐Based Inorganic–Organic Hybrid Particles

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